Barium Dichromate, BaCr2O7

Barium Dichromate, BaCr2O7, is obtained by heating together solid chromic acid and moist, freshly precipitated barium chromate mixed with potassium chromate and potassium dichromate, or by boiling freshly precipitated barium chromate with chromic acid and nitric acid, or, finally, by decomposing the chromate with dilute sulphuric acid. It crystallises in slender, yellowish-brown, rhombic prisms as BaCr2O7.2H2O, the 2 molecules of water being lost at about 100° C. Barium dichromate is decomposed by water, giving the chromate.